[Feat] Add Fast orchestrator to Discord

[roomote-roomote]

​Opened on behalf of @daniel-lxs. Follow up by mentioning @roomote-roomote, in the web UI, or in Slack.

What changed

• Added /fast request:<request> as a top-level Discord orchestrator entry point that works without an active task.
• Let the shared fast agent answer directly or launch a fresh Discord task thread, with Discord-specific lifecycle and reply behavior.
• Registered the Discord command and aligned help text, public documentation, mock runbooks, examples, and eval scenarios with the slash-interaction flow.
• Made /fast the canonical Slack spelling while retaining !fast as a compatibility alias.
• Applied Default messages to fast mode to eligible ordinary Slack and Discord messages, including configured Discord auto-start channels.
• Preserved active-task context when ordinary Discord thread or DM messages enter Fast mode so follow-up instructions continue the existing task correctly.
• Kept Fast mode out of the web task composer until a dedicated top-level web experience is designed.

Why this change was made

Fast mode is an orchestrator that decides whether to answer or delegate work, not a mode entered inside an existing task. Users who choose Fast mode as their communications default should get that behavior consistently across supported Slack and Discord entry points without losing each provider's explicit commands or conversation semantics.

Impact

Linked Discord users can invoke /fast from a DM, channel, or thread, receive a direct answer when no task is needed, and get a new task thread when execution is appropriate. When the deployment setting and personal preference are enabled, eligible ordinary Discord DMs, mentions, thread replies, and configured auto-start channel messages now enter the same orchestrator by default. Slack keeps canonical /fast, legacy !fast, and its existing defaulted-message continuation behavior. Browser proof is not applicable because the shipped behavior lives in communications transport and orchestration rather than the web product surface.

[roomote-community]

No code issues found. See task

• Web /fast now includes visible task conversation context.
• Concurrent web /fast calls now receive unique transcript timestamps.
• Web /fast records task activity at a far-future timestamp.
• Web /fast bounds transcript history in the database.
• Web /fast excludes unflagged legacy workflow and environment wrapper prompts before the database limit.
• Web /fast pages past legacy Slack thread_activity-only prompts before filling its visible context.
• Web /fast can duplicate and omit visible messages when task activity inserts envelopes between the independent OFFSET page queries (the web /fast implementation was removed from this PR).
• Reconciled Discord /fast with Slack-only default routing and sender-specific Fast-agent guidance.
• Applied the personal Fast-mode default to eligible Discord messages while preserving active-task continuation and auto-start routing.

_{Reviewed 565806b}

[roomote-roomote]

Addressed the full review sequence through e1aee1b.

• Web /fast fills its visible context by paging through bounded database result sets and applying the shared transcript visibility resolver to every candidate.
• Explicitly hidden rows, legacy wrapper prompts, and Slack thread_activity-only prompts cannot consume the final 500-message context allowance.
• Concurrent calls receive atomic, millisecond-scale timestamp pairs without overwriting envelopes or skewing task activity.
• Focused database/server tests, affected package typechecks, and the full pre-push suite pass.
• All review threads are resolved and PR metadata is refreshed.

[roomote-roomote]

Updated the branch through b953b26d.

• Merged current develop, including the Slack fast-default behavior and later Fast-mode fixes, without rewriting branch history.
• Kept preference-driven Fast routing Slack-only; Discord /fast remains an explicit top-level orchestrator.
• Preserved Slack /fast as canonical and !fast as a compatibility alias.
• Scoped Slack sender and reaction prompt guidance away from Discord.
• Focused API, cloud-agent, and communication tests passed (165 tests total); affected TypeScript checks and changed-file lint passed.
• The repository pre-push suite passed during validation and again during push.
• PR metadata is refreshed; existing review threads remain resolved.

[roomote-roomote]

Extended the communications Fast-mode default through 565806bf.

• Eligible ordinary Discord DMs, mentions, thread replies, and configured auto-start channel messages now honor the same deployment/user default as Slack.
• Defaulted Discord messages carry active-task context so Fast mode can continue the current task rather than starting unrelated work.
• Explicit Discord /fast, canonical Slack /fast, legacy Slack !fast, and Slack default-message continuation behavior remain intact.
• Shared Discord Fast orchestration keeps interaction replies and ordinary message replies provider-appropriate.
• Focused API coverage passed (129 tests), along with full API typechecking, changed-file lint, docs validation/link checks, and the repository pre-push suite.
• Browser proof is not applicable to this communications transport/routing change.
• PR metadata is refreshed; existing review threads remain resolved.